Optics, because of its inherent parallelism and high bandwidth, has been utilized in the fields of computing, telecommunications and information processing. Today, at the forefront of research and development are interconnection arrangements harnessing the capabilities of optics. Whether using the media of free space or waveguide, transmission rates between electronic devices, optical devices or, on a larger scale, between electronic circuits boards have surpassed the practical limitations of electronic interconnections. Neither encumbered by parasitic capacitance, nor exacerbated by cross talk, electro-magnetic interference or signal delay variations, optical interconnections have afforded higher transmission rates.
The same qualities of optics which allow higher transmission rates, however, place severe interconnection constraints on the designed system's architecture. These constraints to some extent have been overcome by interconnection arrangements as exemplified in U.S. Pat. Nos. 4,705,344 and 4,733,093. These free space or waveguide interconnection arrangements have one thing in common and that is the conversion of an electrical signal to an optical signal for transmission. Typically, an electrical signal needs to be connected to different nodes. Electronic interconnections, mainly because of parasitic capacitance, are limited to a transmission rate of a few hundred megagbits per second. By converting electrical signals to optical signals for transmission via free space or waveguide, optical interconnection arrangements have afforded transmission rates in the gigahertz regime.
FIG. 1 illustrates a typical optical interconnection arrangement known in the prior art to interconnect various points via optical fibers. Electrical signals are converted to optical signals and transmitted to various other nodes by fibers. The optical signals are, then, reconverted to electrical signals by light detecting devices. Although this arrangement is practical for a large number of point to point interconnections, multipoint to multipoint interconnections become unpractical since a large number of optical couplers, taps, and splitters are required and, thus, are constrained by their physical dimensions. Furthermore, these optical couplers, taps and splitters are highly sensitive to the modal distribution of the optical signal; thereby, limiting their use because of modal sensitivity.
Attempts to increase the degree of optical connectivity (number of multipoint ot multipoint interconnections) have focused on the utilization of free space as a transmission media. For example, an array of light emitting devices can be imaged to an array of light detecting devices, establishing high bandwidth interconnections. By placing optical elements such as holograms, diffraction gratings, cylindrical lenses and prisms in the system, arrays of light emitting devices can be imaged to multiple arrays of light detecting devices. See, for example, W. B. Veldkamp et al., Optics Letters, Vol. 11 pp. 303-305 (1986); J. W. Goodman et al., Proc. of the IEEE, Vol. 72, No. 7, July 1984, pp. 850-863; H. J. Caufield, Applied Optics, Vol. 26, No. 19, October 1987, pp. 4039-4040; and A. W. Lohmann et al., Applied Optics, Vol. 25, No. 10, May 1986, pp. 1530-1531. In these optical arrangements, one point is connected over a high bandwidth channel simultaneously to various other points. The degree of connectivity in these instances, however, is outweighed by coupling loss, physical complexity, wavelength sensitivity, or coherence effects that precludes their wide scale commercial use.